Know Your Base Malt
- inexpensive, North American 2 -row isn't well modified
- a 60 minute protein rest won't hurt body or head retention (and might actually help)
- you need to consider kettleDMS as North American 2-row has more of it
- For an excellent podcast on the subject, listen to maltster Joe Hertrich at the MBAA
I’ve had conversations with several sales reps as of late regarding DMS and isobutyraldehyde in their beer and the response invariably comes back to some variation of “we can’t have DMS because well-modified malts don’t have any”. Putting this aside for a moment since it’s not even remotely true, your traditional North American 2-row malt isn’t nearly as well-modified as you think it is.
What do these numbers mean?
North American 2-row malt that most homebrewers use was never intended for making all-malt beers – it was intended for making lagers; specifically, lagers with a large portion of adjunct rice or corn. The diastatic power is typically around 140 °Lintner, (or 475 WK for you Brits) which is a number that represents how many enzymes are available to convert the starch.
For those interested, 100 °Lintner means that 0.1cc of the malt in question infused at 5% can convert all the starch in a 100cc 2% solution in 1 hour at 20°C. Roughly translated, a 100°Lintner malt will be able to convert all the starch available in the barley, but any additional starch will require extra enzymes to convert. Keep that in mind because the average diastatic power of your malt needs to be at the extreme least 40 °L to work and most brewers don't feel comfortable using less than 100°L. That means if you have 30% corn, with a diastatic power of 0 °L and the rest is 2-row, you end up with an average of 93°L, which doesn't leave much wiggle room and a potentially insipid beer. At any percentage higher, say 40%, you would likely switch to 6-row (more protein, more DP) or use thermostable alpha amylase to speed things along.
Anyway, moving on.
North American 2 row has a diastatic power of 140°Lintner, compared to only 110°Lintner for European lager malts, meaning that it’s definitely in the undermodified category and is well suited to these American Adjunct Lagers with at or less than 30% rice or corn.
However, North American craft breweries are using it, but largely to make all-malt ales. A sustained, vigorous boil will still convert SMM to DMS and volatilise it, but there’s a heck of a lot more than most brewers realise. This is because most SMM exists in the embryo and undermodifying malt preserves more embryo (see my article on DMS here.)
That said, what maltsters and brewers refer to when they say “well-modified” is the amount of protein left vs the total soluble protein. Usually it's measured as the Kolbach Index or "S over T". Depending on the species of barley, it can vary from 39 - 50, though most brewers wont' take anything over 40. In North America, most malting barley is either Metcalfe or Copeland, which tends to have fairly high protein compared to European varieties.
Protein content can be a short-hand for a lot of things that directly influence the degree of modification. When protein is broken down, more enzymes are formed. This begins immediately acting upon the gums and hemicelluloses trapping the starch, further lowering the protein content and making the starches more accessible.
© ibd.org.uk, used with permission
If this goes on too long, the barley kernel eats all the starch and your malt is useless, so maltsters dry it at a cool temperature to dehydrate the kernel and fix the amount of enzymes, starches and protein. If this is done earlier in the process, you have more protein and more diastatic power (remember enzymes are made of protein) but the starch is trapped and requires more time in the mash tun and/or protein rests to make it accessible. If this is done later in the process, there is less protein, less starch (since the enzymes have eaten some of it before malting is finished) but the starch is easier to access and well-adapted to homebrew and single temperature infusion setups.
The thing is, this well-modified malt that everyone is talking about starts at around 8% protein and ends at around 11%. Diastatic power is never more than 120°Lintner. It's not meant to be used with a high proportion of adjuncts unless that adjunct is sugar, and even then, you dilute the FAN too much and have to replace it with yeast nutrients. Unfortunately, the large North American malting companies that make the inexpensive 2-row malt don’t make a malt like this (though I've been told they're starting to move in that direction). Those malts are from Britain or Europe and are more expensive due to shipping costs.
I got to visit a few breweries that get bulk 2-row malt delivered. The lowest protein content was 11.3% and the highest was 12.7. According to one head brewer I talked to, those numbers skyrocket during bad years. They’re mainly concerned about beta glucans (which I talk about in mash handling and oxidation) because it tends to gum up the lauter, the filter and lead to oxidation, as well as the extract – which tells them how much sugar you’re going to get out of your malt. That said, extract numbers tended to hover between 77% and 79%, which again, is closer to adjunct lager than all-malt ale malt (ale malt is between 80-82%). You can get well modified North American malt, made from the same variety of 2 row and even from the same malting house, but it's more expensive and it's not always what these brewers are buying.
So what can you, as a home brewer do?
First, understand that if you follow a basic, single infusion mash schedule, you’re going to get roughly the same values you’ve always been getting. However, the excess protein means that keeping it out of your beer is going to be much more difficult, leading to oxidation problems later on. Lauter slowly and handle your mash carefully.
Second, a protein rest is completely doable and won’t harm the body or head retention of your ales. In fact, you’ll actually end up with a much more efficient mash. With high protein levels, 60 minutes is perfectly acceptable and means you can do a double or even triple infusion for those without mash heating available.
Lastly, SMM to DMS is most definitely going to be an issue (as opposed to DMSO to DMS which happens in the fermentor). You can get away with a 60 minute boil – as long as it’s vigorous and well-ventilated (though an old homebrewer who knew his stuff once told me he refused to use it without at least a 70 minute boil).If you’re brewing something like a blonde ale though, I’d recommend a 90 minute boil if you’re looking to further reduce that number.
Thankfully, some Canadian base malt suppliers have detailed records available to the public. You will need some information from your local home brew shop - specifically the item code and lot number that would be delivered with the pallet for Canada Malting/Country Malting at https://countrymaltgroup.com/malt-lot-analysis/
For Rahr base malts, you can get info with the code printed on the bag at https://bsgcraftbrewing.com/MaltAnalysis
For either one, you're going to be looking for an SMM <5 ppm (mg/L), though the closer it is to 5, the longer you're going to want to boil and a KI or SNR of ~40. Closer to 45 with Copeland barley is in the undermodified range and will greatly benefit from a protein rest and a longer boil.